This invention relates generally to motor systems and, particularly, to a power conversion circuit for an electronically controlled motor providing passive power factor correction and harmonic control.
Presently available power supply circuits provide a DC voltage, rectified from an AC source, for powering loads such as a voltage source inverter drive for a brushless DC motor. Typically, a diode bridge rectifier rectifies the AC source voltage and a DC link capacitor provides energy storage for reducing ripple in the rectified voltage. The load, connected across the DC link, is a single or multi-phase electronically commutated motor powered by an inverter bridge, for example.
The power supply circuits known in the art are deficient for several reasons. A soft or hard switching converter may be used, rather than a passive circuit, for improving power factor but such a converter has switching losses associated with it. Other conventional power supply circuits provide power factor correction but do not reduce the level of harmonics in the input current to an acceptable level. In addition, presently available power factor correction circuits for use with a power supply are not easily retrofitted or installed in the DC link of an existing motor.
In general, brushless DC motors are disclosed in, for example, U.S. Pat. Nos. 5,592,058, 5,506,487, 5,491,978, 5,465,019, 5,423,192, 4,933,584 and 4,757,241, all of which are commonly assigned with the present invention described herein and the entire disclosures of which are incorporated herein by reference.